The present invention generally relates to a novel construction for a safety ribbon or core wire. More specifically, the invention relates to a novel safety ribbon for use with a medical guidewire, or a core wire for use with a fixed wire catheter, and the like, which provides substantially symmetric flexibility of the ribbon about an axis of elongation of the ribbon and efficient response to proximally applied forces. Novel methods of manufacturing such a safety ribbon are also provided.
A safety ribbon or core wire is commonly included on the distal end of a medical guidewire or a fixed wire catheter insertable intravascularly into a patient. Such a medical guidewire or catheter has a relatively flexible distal end usually comprising a coiled member for facilitating navigation within the patient's vascular system. A distal end tip, which can be formed by a suitable welding process, for example, is often formed or disposed on the distal end of the coiled member.
As the guidewire or catheter is advanced within a vascular lumen, a juncture of multiple lumens may be encountered, or the vascular lumen may bend or curve within the patient's vasculature. As the guidewire approaches such a juncture or curve, the guidewire must be carefully navigated by a treating physician, clinician, or other medical professional, towards the vascular treatment site. The physician navigates the guidewire by applying forces to a proximal end of the wire which is disposed outside of the patient. These proximally applied forces can be directed for causing rotational, axial, or other desired intravascular movement of the guidewire.
The proximally applied forces are transmitted along the axial length of the guidewire or catheter and are intended to direct or influence the distal end thereof in the desired direction towards the treatment site. This intravascular navigation can become quite difficult and tedious, especially upon consideration of the fact that the guidewire or catheter is inserted into the patient's vascular system at a location, such as the groin, located a significant vascular distance from the treatment site, such as in a coronary or carotid artery. The probability that the distal end will have to be navigated around an increasing number of bends or curves may increase proportionally with the vascular distance between the insertion site and the treatment site.
In an effort to facilitate the navigation of the guidewire or catheter within the vascular lumen, the treating physician often bends or otherwise forms the distal end of the guidewire, specifically the coiled member and possibly the distal end tip, into a predetermined configuration prior to intravascular insertion of the distal end into the patient. The predetermined configuration is usually "J"-shaped, which can facilitate navigation of the distal end of the guidewire in the direction indicated by the distal end of the "J." The "J"-shaped configuration of the distal end can also facilitate selection of a desired branch lumen or vessel. In order to select a desired branch lumen, the treating physician applies a rotational force to the out-of-body proximal end of the guidewire. This force is transmitted along the axial length of the guidewire or core wire to induce rotation of the distal end thereof. The distal end is rotated to point the distal end of the "J" towards or into the desired branch lumen or around the curve or bend. Once the distal end of the "J" is pointed in the desired direction, axially directed forces can be applied to the proximal end to cause axial shifting of the guidewire in the desired direction. Similar navigation procedures are often employed in directing the guidewire or core wire around a sharp bend.
The formation of the coiled member and the end tip, combined with forces exerted thereon during navigation thereof through the patient's vascular system towards the treatment site can stress or otherwise weaken the distal end. In some instances, the resultant stress may be of sufficient magnitude to cause the end tip, the coiled member, or portions thereof to break away from the associated remainder of the guidewire or catheter.
In an effort to reduce the possibility that a portion of the distal end of a guidewire or a fixed wire catheter might break away therefrom, a safety wire or ribbon may be provided. The safety wire is intended to reduce the likelihood of separation of the distal end tip and portions of the coiled member from the guidewire or catheter when breakage occurs during intravascular use. Specifically, the safety wire may be operatively fixedly attached to the end tip, portions of the coiled member, and/or to the remainder of the guidewire or catheter, thereby preventing separation of those elements.
The general construction of a conventional safety wire is well known to those having ordinary skill in the relevant art. Generally, the safety wire comprises a usually flattened, planar distal segment, or element, having a substantially rectangular latitudinal cross section. Round safety wires, can be used, but may be unpopular because they resist bending into a predetermined configuration prior to intravascular insertion, which may be necessary or desirable for navigating the associated device remainder intravascularly as described earlier. In addition, a round safety wire, of a given tensile strength, can be stiffer than a flattened safety wire of similar tensile strength, which may limit the overall flexibility of round safety wire.
An example of a conventional safety wire having a flattened configuration or profile is the device disclosed in the U.S. Pat. No. 3,906,938 to Fleischhacker. Another example of a flattened safety wire, indicated by reference numeral 38 in the disclosure, is shown in the U.S. Pat. No. 5,007,434 to Doyle et al. disposed radially offset from a twisted, elongate shaft of a guidewire. In some constructions, the core wire itself is usually substantially cylindrical in configuration, and a tapered or reduced diameter distal-most segment thereof can be stamped or otherwise flattened to form the safety wire. Other methods of safety wire formation can also be used. The flattened configuration of the safety wire provides the same tensile strength as a round safety wire of equal mass and provides increased flexibility, but the flattened configuration is not as responsive to proximally applied forces as a round configuration, as will be discussed in greater detail shortly.
Opposite ends of the safety wire can be joined to a core wire and the end tip, respectively, by suitable means, such as solder and the like. In some constructions, the end tip may be formed as a part of the safety wire prior to stamping thereof. These constructions allow the distal end of the guidewire or fixed wire catheter to be formed into a predetermined configuration, as described above, relatively easily within a plane orthogonal to a plane defined by the flattened safety wire. However, it is difficult to form the distal end of the guidewire within the plane of the safety wire. In addition, it has been discovered that, irrespective of the plane in which the distal end of the guidewire or core wire is bent or formed, the planar construction of the safety wire tends to orient the bend into the plane orthogonal to the plane of the safety wire (i.e. the plane orthogonal to the plane of the wire is the preferred plane of safety wire or core wire formation). This may be undesirable in some cases, and may complicate navigation of the guidewire or fixed wire catheter within the vascular lumen, as well as limit the intravascular device's ability to select a desired branch lumen because the safety wire is not symmetrically flexible about an axis of elongation of the associated wire and does not efficiently respond to proximally applied navigation forces.
Furthermore, the presence of a limited flexibility safety ribbon in the distal end of a guidewire or of a core wire of a fixed wire catheter may limit performance of the guidewire or the catheter itself. The decreased responsiveness of the distal end to the navigating forces proximally applied by the treating physician may complicate the treatment. The lack of symmetric flexibility and efficient responsiveness of the distal end of the guidewire due to the presence of the safety wire may cause the distal end to "whip" responsive to the combination of forces applied to the proximal end of the guidewire in a navigation effort. It is believed that whipping of the distal end may be caused, or at least magnified by the non-axially symmetric flexibility of the safety wire and, consequentially, the distal end.
Illustrating the phenomenon of whipping of the distal end by example, the guidewire is intravascularly inserted into the patient. As the guidewire moves axially within the vascular lumen, the outer surface of the guidewire contacts the interior surface of the vascular lumen. Multiple bends and/or curves in the lumen can increase the contact between the guidewire and the interior surface of the vascular lumen. The contact generates a resultant force on the guidewire which can attenuate or oppose the proximally applied navigation forces, thereby inhibiting intravascular navigation of the guidewire.
Once the resultant force has achieved sufficient magnitude, the distal end does not move fully responsive to the proximally applied forces because of the attenuation of those forces by the contact-generated friction between the wire and the vascular lumen interior surface. For example, it has been empirically determined by experiment that a ninety degree rotation of the proximal end of a guidewire having a conventional safety ribbon may only result in a ten degree intravascular rotation of the distal end of the guidewire. This is an example of inefficient responsiveness of a distal end to proximally applied forces. In order to navigate the guidewire in the desired direction towards the intravascular treatment site, the treating physician applies increasingly more force (i.e. increasing degrees of rotation) to the proximal end in an effort to overcome the resultant force and to direct the distal end of the guidewire as intended.
If the proximally applied forces achieve a sufficient magnitude, that is, sufficient to overcome a static coefficient of friction between the relevant length of the guidewire and the contacted portion of the vascular lumen interior surface, the distal end whips around, or moves in response to the combined effects of the proximally applied forces. This motion is similar to the release of a wound spring. This whipping is undesirable, may make certain treatment sites difficult to reach, may complicate the procedure the physician is attempting to perform, and may be traumatic to the particular portion of the vascular lumen adjacent the whipping distal end. Similar whipping may occur with the distal end of a fixed wire catheter and other devices, and may also occur when a guidewire is rotated in a lumen within a catheter, or atherectomy device, for example.
The present invention provides a novel safety ribbon or core wire construction which is intended to solve some, if not all of the problems presented by the prior art safety ribbons or wires. Specifically, the novel construction of the safety ribbon can reduce the adverse effects of whipping while increasing navigation-facilitating flexibility and responsiveness to proximally applied forces of the distal end of a guidewire, a fixed wire catheter, and the like. A novel method of manufacturing safety ribbons is also provided.